The present invention relates to video signal coding methods and, more particularly relates to such methods which are suitable for use in transmitting a moving picture video signal.
Conventionally, in a moving picture video signal communication system, such as a conference system for a video telephone system, a moving picture video signal is transmitted to a remote point via a transmission line. It has been proposed to efficiently utilize the limited capacity of the transmission line by transmitting less than all of the successive frames of the signal according to a so-called frame skipping process. The receiver reproduces the frames that have been skipped by the transmitter by interpolation based on picture information for the frames preceding and following the skipped frames with the use of motion vectors transmitted in place of the skipped frames (refer to Japanese Patent Publication No. 60-28392).
Since the motion vectors include less information than complete frames, it is theoretically possible to achieve efficient transmission of significant moving picture information in this manner. In practice, however, it is not always possible for the transmission apparatus to generate accurate motion vector information in the frame skipping process, and in the event that inaccurate motion vectors are transmitted in this fashion, the pictures reproduced by interpolation at the receiver can be objectionably poor in quality.
One type of transmission apparatus codes moving picture information in the form of unitary transmission blocks each including, for example, eight pixels per line by eight lines of the video signal to be transmitted. With the use of such apparatus, the contents of the pictures generated by interpolation at the receiver can become discontinuous in the event that the motion vectors for the transmitted unitary blocks are inaccurate and pictures reproduced with such motion vectors are likewise objectionably poor.